The method of producing 1,4-butynediol by the reaction of formaldehyde and acetylene using a copper acetylide complex as a catalyst is, of course, well known and has been used for many years. It is also well known that this reaction produces cuprene, which tends to clog filters and affects the process adversely.
One method commonly used to inhibit cuprene formation during the reaction is to conduct it in the presence of bismuth, either in elemental form or in the form of a bismuth compound. In Kirchner U.S. Pat. No. 3,650,985, for example, it is demonstrated in Example 39 that bismuth oxycarbonate can be used as a cuprene inhibitor by mixing it, in the initial stage of the process, directly with the basic copper carbonate (malachite) used to form the copper acetylide catalyst. While bismuth used in this way does inhibit cuprene formation, it tends to separate from the catalyst after a time, which leads to unsatisfactory results.
One method of dealing with the separation of bismuth from the catalyst is shown in Belgian Pat. No. 825,446, according to which bismuth is uniformly dispersed in a malachite precursor, and subsequently in the copper acetylide catalyst itself, by first preparing hydrated copper carbonate particles, nucleating and converting these particles to malachite by heating them, and then growing agglomerates of malachite containing bismuth oxycarbonate uniformly dispersed therein by adding solutions of a copper salt, a bismuth salt and an alkali metal carbonate to a water slurry of the malachite. This malachite is easily converted to a copper acetylide catalyst.
While the bismuth compound in a catalyst thus produced tends to stay in place, the catalyst is composed of agglomerates of angular crystals which are degraded by attrition as the butynediol reaction proceeds, which interferes with its efficiency.
This problem, as well as the others just mentioned, is minimized by the use of the malachite and copper acetylide catalyst produced according to this invention, whose agglomerates are spheroidal and contain uniformly dispersed bismuth oxycarbonate.
The spheroidal agglomerates of malachite can be made according to the invention by first forming a mass of hydrated copper carbonate by bringing together, with mixing, an aqueous solution of a cupric salt, an aqueous solution of a bismuth salt and an aqueous solution of an alkali metal carbonate or bicarbonate. This mixture is then held, without stirring or agitation, at a temperature of less than about 55.degree. C., whereupon the spheroidal agglomerates of malachite crystals form.
These agglomerates can, in turn, be converted to copper acetylide complex by slurrying them in water and then subjecting them to the action of the acetylene and formaldehyde.